I'm baffled. No sound through external speakers with Apple TV. Help?

This has me stumped. I was watching a Netflix show and everything was fine. Sound was great, picture was great. I realized I'd seen the episode, so went out and chose another episode. When it started, there was no sound. I tried other apps on Apple TV. Same thing - no sound.

Here's my set up: I have a Sony receiver with 3 external speakers (old school - with speaker wire). The receiver is connected to the TV via an audio cable. The TV (also Sony) is connected to the Apple TV via HDMI through the TV's HDMI (Arc) port.

I tried switching the audio to Apple TV's temporary audio setting, to my Home Pods and that DID work - sound does play through the Home Pod speakers (I tried a couple in different rooms). I also switched to the TV's analog antenna to see if that would work and it did. The speakers through the receiver, connected to the TV (not via Apple TV) DID play the broadcasted sound.

I also tried restarting the system, I tried unplugging it and plugging it back in, I tried unplugging the HDMI and audio cables and plugging them back in but nope. I also tried switching different inputs. Also nope. No sound.

I'm absolutely baffled. Anyone have any ideas??